The invention relates generally to the controlled formation of cavitation bubbles that serve as autonomous chemical mini-reactors and use the energy released during implosion of these bubbles to rapidly alter complex hydrocarbon mixtures.
More particularly, the invention relates to modification of conventional and non-conventional oil by a flow-through hydrodynamic cavitation and utilizes cavitation bubble energy for improving homogeny, viscosity, API (American Petroleum Institute) gravity and other physical properties. This invention may find applications in the oil/fuel industry and synthetic chemistry
Moreover, the present invention relates to a method that subjects petroleum, liquefied shale oil and complex mixtures of hydrocarbons to flow-through hydrodynamic cavitation for a period of time sufficient for alteration of chemical composition, conversion of compounds, obtaining upgraded product with higher yield of distillate fuels.
Oil is a naturally occurring non-renewable source of energy. Similar to other fossil fuels, such as coal and natural gas, it formed from the fossilized remains of plants and animals. Over millions of years, the decay has been translocating into the Earth's crust, where it transformed into oil under heat and pressure.
Apart from conventional oil, produced by the traditional well method, non-conventional oil is produced by very different methods. Sources of non-conventional oil include among others tar sands (oil sand), oil shale and heavy oil. The extraction of oil from sands requires either strip mining or in situ processing with steam and caustic soda. The shale oil contains kerogen, which can be converted into fuels. It was estimated that only 30% of the shale oil deposits meet the economic requirement of 25 gallons of oil per 1 ton of shale, of which only 15% is presently recoverable. The refinement of shale oil is very difficult and requires large quantities of gas and water, which negatively affects its economic value. Heavy oils are very viscous, ranging from heavy molasses to solids at ambient temperature and cannot be transported and refined by conventional methods. They may contain high levels of sulfur, trapped gases and heavy metals and possess a specific gravity similar to that of water.
Oil is a non-uniform fluid and consists of heavy compounds dispersed in light crude, ranging from straight and branched chain and cyclic saturated and unsaturated hydrocarbons to complex aromatics and asphalt (bitumen). Bitumen is usually called the hydrocarbon content of heavy oils and tar sand deposits. It is black, highly viscous, sticky, and soluble in carbon disulfide.
Asphalt is a colloid, with asphaltenes as the dispersed phase and maltenes as the continuous phase. Asphaltenes consist of condensed aromatics with side chains up to C30, hetero-aromatics with sulfur in benzothiophene rings, nitrogen in pyrrole and pyridine rings, polyfunctional molecules with sulphur, nitrogen and oxygen in the chemical groups such as, for example, thiol, amino and keto, hydroxyl, and carboxylic, correspondingly, and porphyrin-complexes of nickel and vanadium. Maltenes are soluble in n-alkanes (pentane or heptane). They contain straight or branched chain saturated hydrocarbons (saturates), cyclic saturated hydrocarbons (cycloalkanes or naphthenes), resins (smaller analogs of asphaltenes), heteroaromatics of oxygen, nitrogen and/or sulfur (first acidaffins), and straight and branched chain and/or cyclic unsaturated hydrocarbons (olefins, second acidaffins).
Petroleum heavy crudes and residues are suspensions of asphaltene colloids stabilized by resins. The smallest colloid particles that are 2-4 nm in diameter form clusters (asphaltene micelles) with a size of 10-30 nm. Further aggregation leads to the formation of flocs and macrostructures (Evdokimov et al., 2001). Thus, conventional and non-conventional oil are non-Newtonian fluids.
Although the mechanical behavior of fluids is characterized by a constant viscosity, this approach inadequately describes non-Newtonian fluids. The relation between the shear stress and the strain rate of such fluids is nonlinear and often time-dependent. Although a constant coefficient of viscosity cannot be defined for a non-Newtonian fluid, it is possible to define a ratio between shear stress and rate of strain, a shear-dependent viscosity, especially for fluids with no time-dependent behavior. Non-Newtonian fluids are studied by measuring rheological properties and the continuum mechanics calculations.
Since hydrocarbons of different molecular weights and structures boil at different temperatures, crude oil is traditionally separated into fractions via fractional distillation, which has become the main refining technique. The residual heaviest fraction obtained by fractional distillation is called refined bitumen. It boils at 525° C. Oil fractionation is conducted at elevated temperatures and pressures in the presence of hydrogen or steam and zeolite catalysts, which require continuous regeneration. Fluid catalytic cracking (FCC) is the most efficient process for oil upgrading in industrial practice, but high temperature (400-500° C.) and pressure (up to 100 atm) are both required. The harsh conditions and safety considerations place constraints and limitations on refinery's material. These methods are expensive and energy consuming.
Because FCC does not open the aromatic structures, bitumen-derived heavy vacuum distillate or vacuum gas oil (VGO) are poor feedstocks. At the present time, upgrading of bitumen, which is composed primarily of highly condensed polycyclic aromatics and exhibits high heterogeneity and stability, is extremely costly. To increase yield of gasoline, multi-ring aromatic compounds are to be saturated to single-ring aromatics in a feed pretreater. Hydrogen added after this step lowers both gasoline yield and octane number.
Distillate fuels such as gasoline, turbo-jet fuel, and diesel fuel are used in internal combustion engines to convert chemical energy and heat into mechanical energy. Gasoline is a fuel designed for the Otto-cycle 4-stroke engine. It contains hydrocarbons with a carbon number ranging from 4 to 10 (C4-C10). Other distillate fuels include diesel, kerosene, turbo-jet fuel, and heating oil. Diesel has a lower boiling point than gasoline and is less costly in production. Instead of spark plugs, the diesel engine relies on compression and the heating of air to cause ignition. However, high levels of contaminants in engine exhaust gas require diesel fuel to undergo additional purification by filtration, driving its cost up. As with FCC, the methods for upgrading oil and complex hydrocarbon mixtures are performed at high temperature and pressure in the presence of catalysts that must be constantly regenerated. These methods are highly expensive and energy consuming.
It has been reported that elevated pressure and increased temperature supplied by acoustic and hydrodynamic cavitation activate many processes and accelerate a number of chemical reactions. The formation of bubbles in a fluid is easy to observe, when its temperature approaches the boiling point. An increase in the hydrostatic pressure of a fluid will suppress the formation of bubbles. If the fluid is subjected to a sound wave treatment or passes through a hydrodynamic cavitation reactor at a proper velocity, cavitation bubbles form as a result of a decrease in fluid pressure (Bernoulli's principle). The concentration of cavitation bubbles reaches hundreds in a cubic centimeter of the cavitated fluid.
Once the bubbles are created, they can remain stationary restricting the flow and taking up space normally occupied by the fluid. This causes a resistance to the flow and increases the pressure. If the bubbles move and relocate into a high pressure zone, they will implode (reversed Bernoulli's principle) within 10−8-10−6 seconds, resulting in a drastic increase in both pressure (˜1,000 atm) and temperature (˜5,000° C.), and formation of local jet streams with the velocities of 100 m/s and higher (Suslick, 1989; Didenko et al., 1999; Suslick et al., 1999; Young 1999). The sudden collapse releases a significant amount of energy in the form of shock wave, vigorous shearing forces, and localized heating, which either initiate chemical reactions and processes or dissipate into the surrounding fluid. These activate gas phase molecules located in the bubbles and in the surrounding liquid and initiate chemical reactions. In some cases, cavitation bubble implosion is accompanied by emission of ultraviolet and/or visible light making it possible for photochemical reactions to proceed.
The formation of large molecular matrices, arrays and pseudo-polymeric systems play an important role in oil processing, resulting in its high surface tension and viscosity, and non-Newtonian behavior. Any disruption of these large molecular associations, particles, agglomerates or pseudo-polymeric interactions leads to alteration of oil properties.
The cavitation phenomenon is categorized by the dimensionless cavitation number Cv, which can be mathematically represented as: Cv=(P−Pv)/0.5 ρV2, where P is the recovered pressure downstream of a constriction, Pv is the vapor pressure of the fluid, V is the average velocity of the fluid at the constriction, and ρ is the fluid density. The cavitation number, at which cavitation starts, is called cavitation inception number Cvi. Ideally, the cavitation starts at Cvi=1, and there are significant cavitational effects at Cv less than 1 (Gogate, 2008; Passandideh-Fard and Roohi, 2008). Another important term is the processing ratio, which is the number of cavitation events in a unit of flow.
While extreme pressure or tremendous heat can be disadvantageous, the outcome of the controlled treatments is often highly beneficial. Lin and Yen (1993) carried out cracking of asphaltenes, which are refractory for FCC and deactivate catalysts even in mild conditions, using ultrasound cavitation, sodium borohydride as a hydrogen source, and a surfactant to prevent recombination and disproportionation of asphaltene radicals. The hydrogen radicals terminated the free radical reactions and saturated olefins. As a result, 35% asphaltenes were converted into gasoline and resins in 15 min. Conversion of asphaltenes into lighter hydrocarbons increased by 10 times.
One disadvantage of sound wave cavitation technology is its batch environment. This technology cannot be efficiently used in a continuous flow process because the energy density and the residence time would be insufficient for the high production output. For example, the intensity threshold of ultrasound cavitation in water is above 0.3 W/cm2. Sound wave cavitation technology suffers from a number of other drawbacks. Since the effect diminishes with an increase in distance from the soundwave source, the treatment efficacy depends upon container size, i.e., it is lower in large vessels. In addition, alterations in fluid are not uniform throughout the fluid and occur at certain locations, depending on the soundwave frequency and interference patterns. Thus, the efficacy of sound cavitation treatment is further reduced. While the previous uses of cavitation provided by sound waves in acoustic (20 Hz-20 KHz) and in ultrasonic (>20 KHz) ranges claim to improve the oil refining yield, they do not offer an optimized method for producing improved fuels.
It has been reported that both physical and chemical properties of petroleum products can be altered by subjecting them to cavitation in a pulsed rotor unit (Promtov, 2008). The treatment improves the quality of fuels.
It is known that cavitation can be created in fluids by means of various hydrodynamic devices. See, for example, U.S. Pat. No. 6,705,396 to Ivannikov et al., U.S. Pat. Nos. 7,207,712, 6502,979 and 5,971,601 (Kozyuk) which all describe hydrodynamic cavitation devices and their uses. U.S. Pat. No. 7,338,551 to Kozyuk discloses a device and method for generating bubbles in a fluid that passes through a first local constriction of a hydrodynamic cavitation device at a velocity of at least 12 m/sec and is then mixed with a gas to enhance implosion.
According to the invention of U.S. Pat. No. 6,227,694 to Mitake et al. two or more substances are reacted through the collision of a jet flow of one reactive substance against a jet flow of another substance at the velocities of 4 m/sec or higher followed by furious turbulence and cavitation. To cause a uniform reaction within a short time, the substances are introduced from different passages and collided against each other at high flow rates. This method is advantageous for producing dispersions of submicron-sized particles.
The cavitation phenomenon is more dramatic in viscous fluids. If oil flow moves at a high speed causing the absolute pressure of the oil to drop below the vapor pressure of hydrocarbon(s) contained in it, cavitation takes place. Cavitation separates the “liquid” phase (high-boiling-point hydrocarbons and their particles in liquid hydrocarbons) from gases that are within the oil (entrapped gases, water vapor and vapors of the affected hydrocarbons). Small particulates and impurities serve as the nuclei for the cavitation bubbles that vary in size from 100 nm to a few millimeters in diameter.
U.S. Pat. No. 6,979,757 to Powers describes a method for utilizing whole crude oil as a feedstock for the pyrolysis furnace of an olefin production plant, wherein the preheated feedstock is subjected to mild thermal cracking assisted with controlled cavitation until substantially vaporized, the vapors being subjected to severe cracking in the radiant section of the furnace.
Another cavitation-based approach illustrated in U.S. Pat. No. 5,969,207 to Kozyuk uses a flow-through passage accommodating a baffle body that generates a hydrodynamic cavitation with the degree of cavitation of at least one to initiate chemical transformations and change qualitative and quantitative composition of liquid hydrocarbons. Microcracking of only liquid hydrocarbons results from the collapse of cavitation bubbles within a hydrodynamic cavitation field that changes the qualitative and quantitative composition of the mixture of only liquid hydrocarbons without using catalyst.
Oils and fuels often contain microorganisms that degrade their constituents, multiply and become an issue, especially in marine transportation. There are many technologies for sterilization of liquids, such as heating, autoclaving, treatment with antibiotics, disinfection with chlorine, ozone, permanganate and other reagents, filtration, sorption, ultraviolet and X-ray irradiation. However, most of these technologies are not applicable to oil and petroleum-related products. For instance, UV-disinfection of fluids is strongly dependent upon the uniform exposure of the target species. Due to the high opacity and shading effect of suspended particulates UV-sterilization usually exhibits low potency in oils. Uniform exposure can be achieved in a UV shockwave reactor equipped with an inner rotor with surface cavities surrounded by a quartz housing. Such device increases irradiation dose from 97 J/m2 at 0 rpm to 742 J/m2 for speeds above 2,400 rpm (Milly et al., 2007a; Milly et al., 2007b). Although the rotor cavitation may inactivate bacteria, bacterial spores, yeast, and yeast ascospores, its lethality strongly depends on the speed of the rotor and can be improved by preheating of fluid instead of increasing pump pressure.
U.S. Pat. No. 6,200,486 to Chahine et al. discloses another application of cavitation for quality control of fluids. This approach utilizes cavitation in shear zones associated with the jet nozzle to reduce contaminants in liquids. The jet-induced cavitation triggers chemical reactions (oxidation and reduction), which leads to decomposition and destruction of contaminants and unwanted microorganisms.
Yet another U.S. Pat. No. 7,247,244 to Kozyuk describes a process and device for lowering the level of organics in fluids with the help of oxidizing agents that are introduced into a local constriction in a flow-through chamber. Implosion of cavitation bubbles, which contain and/or are associated with the oxidizing reagents, can be accompanied by emission of ultraviolet light, ionization, generation of hydroxyl radicals, and accelerated decomposition and/or oxidation of the organic matter.
At the present time, with energy costs rising rapidly, it is highly desirable to shorten processing times and lower energy consumption to secure as large a profit margin as possible. However, the prior art techniques do not offer the most efficient method of upgrading non-Newtonian fluids in the shortest amount of time possible.
A need, therefore, exists for an advanced method and a flow-through system of conventional and non-conventional oil treatment and hydrocarbon mixture processing, with a minimal time treatment and energy cost, resulting in products with improved characteristics that can be refined with a higher distillate fuel yield and are easier to handle.
The advanced, compact, and highly efficient device is particularly desirable at mining locations and at refineries, where throughput is key. The present invention provides such a method and a device while delivering upgraded products within short time.